1. Field of the Invention
This invention relates to engine retarders of the compression release type. More particularly, the present invention relates to a mechanism which automatically modifies the valve train lash when the engine is placed in the retarding mode and simultaneously provides for a prompt reclosing of the exhaust valve following the compression release event.
2. The Prior Art
Engine retarders of the compression release type are well-known in the art. Such retarders are designed to convert, temporarily, an internal combustion engine of the spark ignition or compression ignition type into an air compressor so as to develop a retarding horsepower which may be a substantial portion of the operating horsepower normally developed by the engine.
The basic design for the engine retarding system of the type here involved is disclosed in the Cummins U.S. Pat. No. 3,220,392. In that design, an hydraulic system is employed wherein the motion of a master piston actuated by an appropriate intake, exhaust or fuel injector pushtube or rocker arm controls the motion of a slave piston which opens the exhaust valve of the internal combustion engine near the end of the compression stroke whereby the work done in compressing the intake air is not recovered during the expansion or "power" stroke but, instead, is dissipated through the exhaust and cooling systems of the engine.
Various improvements have been made in the original design shown in the Cummins U.S. Pat. No. 3,220,392. Laas U.S. Pat. No. 3,405,699 discloses a device which unloads the hydraulic system whenever excess motion of the slave piston tends to open the exhaust valve too far and hence risk damage to the components of the engine.
Egan U.S. Pat. No. 4,150,640 discloses a pressure relief valve in the high pressure hydraulic system which limits the maximum pressure attainable in that system. Sickler U.S. Pat. No. 4,271,796 discloses a pressure relief system for a compression release engine retarder wherein a bi-stable relief valve and a damping mechanism rapidly drops the pressure in the hydraulic system to a predetermined low level whenever an excess pressure is sensed in the hydraulic system, thereby obviating the risk of damage to various components of the engine valve train mechanism.
Johnson U.S. Pat. No. 4,384,558 discloses a mechanical mechanism incorporated into the slave piston and adapted to decrease the valve train lash during the retarding mode of operation. Custer U.S. Pat. No. 4,398,510 discloses an hydro-mechanical timing advance mechanism located in the slave piston adjusting screw which modifies the valve train lash during the retarding mode of engine operation.
Mayne et al. U.S. Pat. No. 4,423,712 discloses a spool valve located in the slave piston adjusting screw which cooperates with a reservoir located in the slave cylinder and unloads the slave piston at the end of the compression release event to insure prompt reclosing of the exhaust valve.
Cavanagh U.S. Pat. No. 4,399,787 discloses a mechanism which senses the force required to hold open an exhaust valve during a compression release event and releases the hydraulic pressure when this force has decreased substantially, thereby causing the exhaust valve to close.
Jakuba et al. U.S. Pat. No. 4,473,047 relates particularly to engines equipped with dual exhaust valves and an engine retarder of the compression release type and discloses apparatus adapted to open only one of the dual exhaust valves during the retarding mode of operation while permitting both valves to be opened during normal engine opera- tion.
As set forth in the patents referred to above, the compression release engine retarder utilizes portions of the existing engine valve train and fuel injection mechanism to open the exhaust valves near the end of the compression stroke. In order to avoid undesirable loading effects on the valve train mechanism, particularly when it is desired to open only one of a pair of dual exhaust valves during the compression release event, it is important to assure that the exhaust valves close promptly after the compression release event has been completed. However, it is also desirable to modify the lash in the valve train mechanism during retarding in order to improve the timing of the compression release event so as to maximize the retarding horsepower which can be developed by the engine.